Search gender: all male female コガ Japanese Boy Names Variations. 1 names found. gender: all male female Name: koga Katakana: コガ 0 Kanji: 古賀 Meaning: 古Old 賀Rejoice. Celebrate. You can save your favorite names with NAZUKE PON > About Japanese Names > Search Japanese Names By Kanji > コガ Japanese Boy Names Variations.